The present invention is directed to liquid measuring systems in general, and more specifically, to a liquid measurement system including interface apparatus for sharing the excitation and signal processing of an ultrasonic transducer and temperature measuring device remotely located at a liquid container.
Present liquid measurement systems of the ultrasonic variety utilize an ultrasonic transducer disposed at the liquid container for measuring the level of liquid in the container. The ultrasonic transducer is excited to generate ultrasonic pulses directed at the surface of the liquid level and for receiving echoes from the surface of the liquid level that are converted into corresponding echo signals. These systems generally include a temperature measuring device, like a resistance temperature device or RTD, for example, disposed at the container in contact with the liquid in close proximity to the ultrasonic transducer. When the RTD is excited, it generates a response signal representative of the temperature of the liquid that is used along with the echo signals for the determination of the liquid level in the container.
While the ultrasonic transducer and its temperature measuring device are located at the liquid container, the apparatus for exciting and signal processing each such device is generally located remotely from the container. Where the liquid container is a fuel tank on-board an aircraft, the exciting and processing apparatus may be located anywhere from twenty to three hundred feet from the fuel tank. In addition, each device includes its own dedicated apparatus and cabling and on-board commercial aircraft in particular, there may be thirty to forty or more of these devices. Thus, in the aircraft industry, this individually dedicated apparatus and cabling represents a heavy burden in volume and weight as well as cost of labor, maintenance and fuel consumption. Accordingly, it is desirable, especially for aircraft applications, to reduce the dedicated apparatus and cabling for each such device.
In accordance with the present invention, a liquid measurement system includes interface apparatus for sharing the excitation and signal processing of an ultrasonic transducer remotely located therefrom at a liquid container and of a temperature measuring device disposed in close proximity to the ultrasonic transducer for measuring the temperature of tile liquid threat. The ultrasonic transducer is excited to generate ultrasonic pulses directed at the surface of the liquid level in the container and for receiving ultrasonic echoes from the liquid level that are converted into corresponding echo signals. The temperature measuring device is excited to generate a response signal representative of the temperature of the liquid in close proximity to the ultrasonic transducer. The interface apparatus includes a first means for generating first excitation signals for tile ultrasonic transducer, second means for generating second excitation signals for the temperature measuring device, a common conduction path coupled to both of the ultrasonic transducer and the temperature measuring device for conducting the first excitation signals to the ultrasonic transducer and the corresponding echo signals therefrom, and for conducting the second excitation signals to the temperature device and the response signals therefrom, and an interface circuit coupled between the first and second means and the common conduction path for governing the conduction of the first and second excitation signals over the common conduction path and for providing a balanced interface for receiving both of the echo signals and response signals from the common conduction path. In accordance with another aspect of the present invention, the liquid measurement system includes a processing means coupled to the interface circuit for receiving the echo signals and the response signals therefrom for determing liquid level in the container based on the received signals.